1. Field of the Invention
The present invention generally relates to monolithic LC components, and more particularly, to a monolithic LC component, such as a band-pass filter, including a plurality of LC resonators.
2. Description of the Related Art
A known monolithic LC component includes a monolithic LC band-pass filter constructed as shown in FIGS. 7 and 8. A monolithic LC band-pass filter 1 includes, as shown in FIG. 7, ceramic sheets 2-8 provided with inductor via-holes 10a-10d and 11a-11d, resonating capacitor patterns 13 and 14, input/output capacitor patterns 17 and 18, and shield patterns 20 and 21.
The ceramic sheets 2-8 are laminated, and protective ceramic sheets are provided on the upper surface of the ceramic sheet 2 and the lower surface of the ceramic sheet 8. Thereafter, the ceramic sheets 2-8 with the protective sheets are fired, thereby producing a monolithic element 24 shown in FIG. 8. An input terminal P1, an output terminal P2, and ground terminals G1 and G2 are provided on the monolithic element 24. The input/output capacitor pattern 17 is connected to the input terminal P1, while the input/output capacitor pattern 18 is connected to the output terminal P2. The shield patterns 20 and 21 are connected to the ground terminals G1 and G2.
In the band-pass filter 1, the inductor via-holes 10a-10d and 11a-11d are connected to each other in the direction in which the ceramic sheets 2-8 are laminated (in the Z-axis direction), thereby forming columnar inductors L1 and L2, respectively. The resonating capacitor patterns 13 and 14 are disposed on the X-Y plane of the ceramic sheet 4, and face the shield pattern 20 with the ceramic sheets 2 and 3 held therebetween, thereby defining resonating capacitors 2 C1 and C2, respectively. The columnar inductor L1 and the resonating capacitor C1 define an LC resonator Q1, while the columnar inductor L2 and the resonating capacitor C2 define an LC resonator Q2. The LC resonators Q1 and Q2 are arranged such that they are separated from each other with a predetermined space therebetween, and are electromagnetically coupled to each other with a suitable coupling coefficient. The input/output capacitor patterns 17 and 18 face the resonating capacitor patterns 13 and 14, respectively, with the ceramic sheets 4 and 5 held therebetween, thereby defining an input capacitor C3 and an output capacitor C4, respectively.
When narrow-bandwidth filtering characteristics are required in the above-configured band-pass filter 1, the distance between the LC resonators Q1 and Q2 should be increased so as to inhibit electromagnetic coupling therebetween. However, to increase the space between the LC resonators Q1 and Q2, the LC resonators Q1 and Q2 must be located at the edges of the band-pass filer 1. This weakens the shielding effect of the shield patterns 20 and 21 on the LC resonators Q1 and Q2, and thus, the Q characteristics of the LC resonators Q1 and Q2 are lowered. Conventionally, therefore, the band-pass filter 1 must be enlarged in order to maintain the characteristics of the LC resonators Q1 and Q2 at a high level.
In order to overcome the problems described above, preferred embodiments of the present invention provide a compact monolithic LC component in which high Q characteristics of resonators can be achieved while meeting the requirements of narrow-bandwidth filtering characteristics.
According to a first preferred embodiment of the present invention, a monolithic LC component includes a monolithic element defined by laminated insulator layers, a plurality of electromagnetically coupled LC resonators each defined by an inductor and a capacitor disposed in the monolithic element, the inductor being defined by connecting via-holes in a direction in which the insulator layers are laminated, a coupling adjusting conductor defined by connecting via-holes in the direction in which the insulator layers are laminated, wherein the coupling adjusting conductor is disposed between at least two of the adjacent LC resonators so as to adjust a coupling coefficient between the adjacent LC resonators and the coupling adjusting conductor is grounded.
As discussed above, the coupling adjusting conductor defined by connecting via-holes in the direction in which the insulator layers are laminated (in the X-axis direction) is disposed between two adjacent LC resonators. Thus, the mutual inductance between the inductors of the adjacent LC resonators can be adjusted by the coupling adjusting conductor, thereby changing the coupling coefficient between the adjacent LC resonators. It is thus possible to inhibit the coupling coefficient of the adjacent LC resonators without the need for increasing the distance therebetween. Accordingly, the LC resonators do not have to be located at the edges of the LC component. As a result, the Q characteristics of the LC resonators can be maintained.
The inductors of the adjacent LC resonators, between which the coupling adjusting conductor is interposed, may be electrically connected to each other by a coupling adjusting conductor pattern disposed on the surface (X-Y plane) of the insulator layer. With this arrangement, the range of adjustments of the coupling coefficient can be extended.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.